Microwave and millimeter wave systems commonly use space diversity and frequency reuse in order to more efficiently provide coverage over a service area. In such systems the space diversity and frequency reuse can be accomplished with directional antennas, as such the system's operation is greatly impacted and dependent upon the patterns formed by the directional antenna. Signals propagating or existing outside the desired antenna direction or pattern can degrade system performance. Signals originating from behind or the back hemisphere of antenna are usually coupled into the antenna by signals scattering off of the outside edge of the antenna. The strength of these spurious signals relative to the desired signals is commonly characterized as the F/B ratio (the radiated energy from the front/the radiated energy from the back), where the larger value is more desirable, at least for directional antennas.
Previous solutions to reducing these spurious signals and improving F/B ratio and thus the overall efficiency of a system, have used adjacent waveguides sized to allow the propagation of the TE10 mode only. These solutions used the waveguides as chokes to create nulls in space that are not oriented along the outside edge where the leaked E-Field is propagated out away from the edge but not nulled along the edge of the antenna. Other previous solutions include the use of absorbers to attenuate the signals propagating from the side and around the back of antennas, or large metallic shields in an effort to increase the F/B ratio. However, in addition to the fact these approaches are generally less effective, these approaches require waveguides, absorbers, and/or shields that are of considerable size often on the order of many wavelengths λ. As directional antennas are usually clustered at a hub positioned at a substantial height above the ground, dimensional size and weight are by no means a trivial matter. Thus there is a need to more effectively increase the F/B ratio in direction antennas without substantially increasing the dimensional size, weight and complexity.
In order to obviate the deficiencies of the prior art as describe above, it is an object of the disclosed subject matter to provide a novel isolation shield for improving F/B ratio for a directional antenna radiating a electromagnetic wave with a wavelength of λ. The system including a waveguide adapted for attachment to at least one side of the directional antenna, the waveguide defining a channel spanning and positioned adjacent to a side of the directional antenna. The channel having a width as a function of λXMT, thus providing a null E-field within the channel that is adjacent to an edge of the directional antenna. The isolation shield thereby improving the F/B ratio of the directional antenna.
It is another object of the disclosed subject matter to provide a novel directional antenna system configured for radiating a c/λ Hertz signal, where c is generally the speed of light. The directional antenna system including a directional antenna defined by an outer edge and a waveguide adjacent to the outer edge. The waveguide is configured to excite a TE20 mode at an wavelength λ within the waveguide.
It is still another object of the disclosed subject matter to provide an improved method for improving the F/B ratio for a directional antenna with an adjacent waveguide. The directional antenna configured to radiate a λ wavelength signal. The improvement comprising: dimensioning the waveguide to excite a TE20 mode for the λ wavelength signal and creating a null, along the edge of the directional antenna, in an E-field leaked from the antenna.
It is yet another object of the disclosed subject matter to provide an antenna cluster with an improved antenna pattern. The antenna cluster having at least two co-located directional antenna systems, one configured for radiating a c/λ1 hertz signal in one direction and another configured for radiating a c/λ2 hertz signal in another direction. In the antenna cluster one of the antenna systems comprises a directional antenna defined by an outer edge and a waveguide adjacent to the outer edge of the antenna. The waveguide is dimensioned to excite a TE 20 mode at an wavelength λ2, of the other antenna, within the waveguide.
It is also an object of the disclosed subject matter to provide a novel directional antenna system configured for radiating a horizontally polarized signal with at c/λ hertz. The direction antenna system including a directional panel antenna defined by an outer edge for radiating the signal, the outer edge formed by two side edges, a top edge and a bottom edge. The directional antenna system also includes a waveguide adjacent to one of the two side edges and forming a channel parallel to the side edge. The waveguide is dimensioned to excite a TE 20 mode within the channel for λ wavelength signal.
The disclosed subject matter presents embodiments with simple waveguide elements that can be designed in or added on to an existing antenna to substantially improve the antenna performance, especially the F/B ratio without the associated drawbacks of the prior art.
These and many other objects and advantages of the disclosed subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal or the claims, the appended drawings, and the following detailed description of the preferred embodiments.